A conventional type of plate heat exchanger use heat transfer plates fitted with gaskets that seal off each channel from the next, and direct the fluids into alternate flow channels. This type of plate heat exchanger is used throughout industry as standard equipment for efficient heating, cooling, heat recovery, condensation and evaporation.
Such a plate heat exchanger consists of a series of thin corrugated heat exchanger plates fitted with gaskets. The plates are then compressed together between a frame plate and a pressure plate in order to create an arrangement of parallel flow channels. The two fluids flow in alternate channels which gives a large surface area over which the transfer of heat energy from one fluid to the other can take place. The channels are provided with different corrugated patterns designed to induce maximum turbulence in both the fluid flows in order to make heat transfer as efficient as possible. The two different fluids normally enter and leave at the top and bottom of the heat exchanger, respectively. This is known as the counter-current flow principle.
One advantage with heat exchangers having gaskets compared with brazed heat exchangers is that it is easy to assemble and separate the heat exchanger plates. This is of advantage e.g. when they need to be cleaned or when the capacity of the heat exchanger is to be adjusted. This is done by simply adding or removing heat exchanger plates when required.
In one type of plate heat exchangers, the heat exchanger comprises one type of plate, which is mounted with every other plate rotated 180 degrees to form two different channels for the fluids, one channel for the cooling medium and one channel for the product that is to be cooled. A sealing is provided between each plate. Such an arrangement is cost-effective and works for many applications. Each plate is provided with ridges and valleys in order to on one hand provide a mechanical stiffness and on the other hand to improve the heat transfer to the liquid. The plates will bear on each other where the patterns of the plates meet each other, which will improve the mechanical stiffness of the plate package. This is important especially when the fluids have different pressures. For this type of heat exchanger, the inlet and outlet opening regions must be adapted so that they work for both channels.
It is also important that the heat exchanger plates are aligned properly in relation to each other, both in the vertical as well as in the horizontal direction. This is especially important for heat exchangers having a high number of heat exchanger plates stacked together, since a small misalignment may multiply with the number of heat exchanger plates. Misaligned heat exchanger plates may result in leakage in a flow channel due to misalignment of the sealing gasket, or even to damage to the heat exchanger.
There are different ways to align the heat exchanger plates. One common way is to use guiding bars, normally at the upper and lower sides of the heat exchanger plates. Such a solution may not give a sufficiently high precision, such that other alignment means are also required. One common solution of obtaining an alignment of the heat exchanger plates is to provide a guiding surface at the corners of the heat exchanger plate.
The corner regions of heat exchanger plates are commonly rounded, i.e. provided with a radius. It is known to provide rounded guiding surfaces at the corners, having a radius with the same centre as the port openings. In this way, the upper edge of one plate bears on the lower edge of another plate when they are stacked. At the same time, the corner region must, apart from guiding the plates, also stabilise the gasket groove around the port opening. The guiding surfaces will thus be rather small, and may comprise only a few small surfaces where the stabilising nuts of one plate bear against the rear side of another plate. This solution may work for larger plates, where there is space enough for a rounded guiding surface. The angle of the rounded guiding surface is normally in the region of up to 70 to 85 degrees.
On smaller plates, there may not be room for such a solution. It may be that there is only room for a guiding surface having a smaller angle or the radius of the guiding surface may have to be rather small. Both these arrangements will deteriorate the possibility to align the plates in a proper way.
U.S. Pat. No. 5,967,227-A disclose a heat exchanger plate having a guiding collar. The guiding collar is concave, having a negative radius compared with the outer corner of the plate.
EP-0 450 822-A1 discloses a heat exchanger plate having a tapered collar included in the guiding bar recessions. The tapered collar, which may be of a somewhat triangular shape, is intended to align the heat exchanger plates.
JP-11287582-A discloses a heat exchanger plate having projecting guiding parts incorporated in the sealing gasket groove around the port openings.
These known solutions show different types of alignment aids that may work well in specific applications. They are however intended for larger heat exchanger plates, where there is space enough to incorporate such solutions. There is thus room for improved guiding means that are also intended for the use on smaller heat exchanger plates.